1. Field of the Invention
The present invention relates to a swash plate compressor incorporated into a refrigerating circuit of an air-conditioning system for a vehicle.
2. Description of the Related Art
A swash plate compressor of this type is disclosed, for example, in Unexamined Japanese Patent Application No. 5-10255. This publicly known compressor includes a cylinder block in which a plurality of cylinder bores are defined and pistons inserted in their respective cylinder bores. These pistons reciprocate in the cylinder bores in response to the rotation of a swash plate. The reciprocation of the pistons performs the process of sucking a refrigerant used in the refrigerating circuit and the process of compressing/discharging the refrigerant, and thus the compressor can supply a high-pressure refrigerant to the refrigerating circuit.
The above-described swash plate is closely sandwiched between a pair of shoes of the piston at its outer periphery, and rotates while sliding against the shoes. In relation to the swash plate, however, the shoes merely sandwich the outer periphery of the swash plate from both sides at in the axial direction of the piston. In other words, the shoes are not restricted by the outer periphery of the swash plate in view of the circumferential and radial directions of the swash plate.
On the other hand, during the rotation of the swash plate, side force is exerted on each piston in a direction perpendicular to the axis of the piston. The strength of the side force is determined by a tilt angle of the swash plate and the sliding resistance between the swash plate and the shoes.
Therefore, the side force causes the piston to press against a part of the inner circumferential surface of the cylinder bore, thus creating non-uniform abrasion of the piston and the inner circumferential surface of the cylinder bore.
In order to prevent the non-uniform abrasion, the swash plate of the compressor disclosed in the above-mentioned publication has an annular groove in each end face thereof, and the shoes are fitted into the annular grooves, respectively. In this case, the shoes relatively slide in the annular grooves according to the rotation of the swash plate, thereby being restricted in their displacement in the radial direction of the swash plate. As a result, in relation to the radial direction of the swash plate, the side force is not exerted on the piston and the no-uniform abrasion of the piston and the cylinder bore due to the side force is reduced.
The outer periphery of the swash plate, however, slides against the shoes at higher speed in the circumferential direction of the swash plate, as compared with the displacement of the piston in the radial direction thereof. For this reason, the side force exerted on the piston in the circumferential direction of the swash plate is greater than that in the radial direction of the swash plate.
Accordingly, even if the annular grooves are formed in the swash plate, it is impossible to sufficiently lessen the side force exerted on the piston, that is, the non-uniform abrasion of the piston and the cylinder bore.
On the other hand, the compressor described in the publication further includes a stopper face that restrains the rotation of the piston around its axis during the rotation of the swash plate. The stopper face is formed at one end of the piston protruding from the cylinder bore, that is, in the outer surface of a tail of the piston that retains the shoes. The stopper face has the shape of a circular arc, and this circular arc extends along the inner circumferential surface of a swash plate chamber or a crank chamber accommodating the swash plate. The stopper face slides against the inner circumferential surface of the crank chamber to allow the reciprocation of the pistons, and on the other hand restricts the rotation of the pistons.
It is very difficult, however, to bring the inner circumferential surface of the crank chamber and the stopper face into closely contact with each other, so that a small gap left-between the inner circumferential surface of the crank chamber and the stopper face is unavoidable. Consequently, during the operation of the compressor, the leading or trailing edge of the tail of the piston in view of the rotating direction of the swash plate hits on the inner circumferential surface of the crank chamber. Such collision not only vibrates the compressor but also increases the noise of the compressor.